Capabilities and Limitations of FireBarriersDr. Vytenis BabrauskasFire Science and Technology, Inc.
Question asked by CPSC• Should CPSC change the regulatory approachfrom a smolder test on bench-scale models to:– An approach that limits fire growth byperformance requirements similar to 16 CFR1633?, or– An approach that requires the use of fire barriers?(for all fabrics, not just Class II fabrics).
Why is CPSC considering changing approachfrom 16 CFR 1634 (2008 smolder standard)?• Problems with scaling??• Difficult to understand this point:– Flaming tests are known not to scale well fromsmall-scale to large-scale, but cigarette tests do.– California has consistently found that mockups dopredict real-chair behavior.“Bench scale performance did not predict full scaleflammability…especially for smoldering ignition”
Smolder testing…• CPSC considers that any regulatory test thatthey adopt needs to accurately control thereal-article hazard and classify the products inthe same way as they behave in full scale.• For tested cigarette mockups, CPSC concludedthat the mockup tests did not always predictthat full-scale chairs will fail by smolderingwhen cigarettes are placed at certain locationson the chair.
…Smolder testing…• They identified these problems:– Two different “standard” foams behaved verydifferently.– Mockups did not have doubled-over fabric layers(which promote smolder), while some realfurniture did.– Full-scale furniture itself showed significantdifferences between supposedly identicalsamples.. . . .
…Smolder testing– Fabric tension may not be well simulated.– Side arms are generally constructed verydifferently from back cushions.– Fire barriers, when tested in mockups using“standard” fabric and “standard” foam do notreproduce the behavior of some actual chairs.
Three possibilities exist• Require full-scale testing of chairs.– Full-scale testing does not seem practicable, sincethere is an enormous number of fabrics used bymost manufacturers.• Stop all standard development• Fix mockup problems…
Improving mockup testing…• Specifications for “standard” foam have not beenadequate.– It is unreasonable to suppose thatdensity, ILD, permeability, etc. would suffice todescribe the smolder propensity.– It should be possible to define specifications for a“standard” foam, but the specifications must include acigarette test.– Smoldering is a chemical phenomenon, and physicaltests do not measure chemical properties.
…Improving mockup testing…• Lack of stringency concerning doubled-upfabrics is simple to fix.– Make mockups use doubled-up fabric.• Specimen-to-specimen variations in full-scalechair construction.– Have to accept this. Upholstered furniture is hand-built and not made on an assembly line.
…Improving mockup testing• Wide differences in construction of realchairs, depending on the exact locale.– Need to select a near-worst-case mockupconfiguration. Then most actual variations willtend to give conservative differences, while thefew opposite results will be rare.• Some smolder barriers behave too well inmockup tests, compared to real furniture.– May need to revisit specifications for “standard”fabric and foam.
Recommendations• Needed improvements in mockup testing forsmolder resistance should not be difficult.– With such modifications, a smolder standardshould prove to be reliable.• I do NOT believe that flame-resistance testingfor barriers is economically justifiable.• I do NOT believe that HRR testing of full-scalefurniture is economically justifiable.
Flame tests or HRR tests are not justified…• CPSC reported that there are about 30“addressable” fire deaths per year from small-flame ignitions.• Added costs would have to be very small tocreate a positive benefit/cost situation.• Economic and engineering analyses on large-flame ignitions are non-existent.• Added costs of producing TB133-type furniturewould be large.• Comfort and choice would be reduced if TB133-type furniture were mandated.
…Flame tests or HRR tests are not justified• Testing to a peak-HRR type requirementwould involve high costs.• A manufacturer may offer thousands of fabricvariations.• Peak HRR is dependent on fabric type– Babrauskas (1983) showed a factor-of-4 effect!• Could not adopt the 16 CFR 1633 strategy ofignoring fabric variations.